IMO questions that are related to blender and have an answer should be answered, regardless of how basic it might seem to experienced users. We all started somewhere and having a resource like the stack exchange makes learning easier.
Yes there is documentation available but, well is sometimes old, poorly written or does not apply to current versions. Video tutorials? Don't get me started on how bad most of them are.
Some other posters will never read a manual no matter what... well that is beyond the scope of this site... Granted some of the questions show amazing laziness, but if the idea is to have this site be a solid reference we should embrace all levels and encourage participation. Hopefully those asking basic questions will come back with more interesting ones as they learn, and teach us something along the way...
Down voting a question discourages participation and makes the site unfriendly. Newcomers feel judged and might look elsewhere for help. The very nature of Blender is about inclusiveness.
What questions should be voted down? Offensive ones, Non questions (like people complaining or venting issues), questions completely unrelated to blender.
It you feel that you absolutely must vote down a question, don't do it without leaving a comment. For all other issues there are tools that seem to work well like closing, marking as duplicate, or asking for clarification.
You don't like the question? It's too obvious for you? Why waste your time on it? Then leave it for someone else to answer. Maybe a newbee can answer newbee questions and get reputation (and courage to ask in turn...)